I don't know if it's possible... I've been looking through the functions in "FE" fore some days know. But one thing that would be handy is the oportunity to make more "Main Librarys" so you can make a more suitable hiarchy from start. Make it more streamlined so you can sort up in some main categories from the top level. Ex; WEBFONTS, GRAPHIC FONTS, TRUETYPE FONTS... just a fealing that having this things sorted from start it will be easier to make groups and categorisation with little less fonts to index everytime you open the different sub cat; OpenType/CFF, OpenType/TT and Truetype.

I think having two or more main libraries is an idea with big disadvantages. Fonts will be distributed among two libraries and 1) you will not be able to find two fonts having the same name of different types if you put them into different libraries (like "My Font 1"/OpenType and "My Font 1"/TrueType). You also will probably need to make backups of all libraries and then have many different ZIP files.The Fonts view can display Library by different ways, so you can display Library having levels: Stype/FontStyle/Weight etc. (You can choose up to million combinations of levels without rearranging any physical fonts on local disk.)

You can switch Library preview hierarchy while all physical library fonts on local disk will not be changed: